1. R. Honegger , in Lichen Biology , ed. T. H. Nash III , Cambridge University Press , Cambridge, UK , 2nd edn, 2008 , ch. 3, pp. 27–39
2. B. Büdel and C.Scheidegger , in Lichen Biology , ed. T. H. Nash III , Cambridge University Press , Cambridge, UK , 2nd edn, 2008 , ch. 4, pp. 40–68
3. Lichen-Like Symbiosis 600 Million Years Ago
4. Fragments of the earliest land plants
5. The oldest fossil lichen